National Instruments SCXI-1102 Application Note
NATIONAL
INSTRUMENTS
®
The Software is the Instrument
®
Application Note 076
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340998B-01
©
Copyright 1997 National Instruments Corporation. All rights reserved.
March 1997
How to Use Thermocouples with an
SCXI-1102 Module
This application note describes how to set up and use the SCXI-1102 with thermocouples. It also describes the
example programs that use the SCXI-1102 to make thermocouple measurements. These example programs are
included on the SCXI Application Examples disk included in the SCXI Getting Started Pack (P/N 777132-01).
You can also download these programs from the National Instruments BBS. These programs, written in
LabVIEW, LabWindows/CVI, and C specifically for the configuration described in this application note, are
easy to understand and use. They serve as a starting point for more complicated programs.
Following the programming instructions, this note includes some useful background information – a brief
description of thermocouple operation and special signal conditioning requirements for thermocouples.
SCXI-1102 Overview
The SCXI-1102 is a 32-channel thermocouple amplifier module. Each of the 32 channels includes a gain
amplifier and lowpass filter. The block diagram in Figure 1 shows the basic function blocks of the SCXI-1102.
Thermocouple
V
out
to DAQ
board or
SCXI bus
Ground
Reference
CJ Sensor
Input
Protection
Gain
(1 or 100)
Multiplexer
SCXI-1102
SCXI-1303
Terminal
Block
32 Channels
+
–
Filter
Filter
+
–
•
•
•
•
•
•
Buffer
Buffer
Figure 1. Block Diagram of the SCXI-1102
Each input channel includes input protection and a lowpass noise filter with a fixed bandwidth of 1 Hz. Each
channel also includes a software programmable gain amplifier that can be set for a gain of 100 (for
thermocouple and other millivolt signals) or 1 (for
±
10 V inputs). The outputs of the 32 amplifiers are